Gas hydrates in deep ocean sediments. Final report 1 April 1981-30 October 1983
1983
The purpose of this research was to elucidate the composition, state, and origin of gas in marine sediments, with particular emphasis on gas hydrates. Gas hydrates are ice-like chlathrate structures in which gases are occluded within a crystalline lattice under appropriate conditions of high pressure and low temperature. Gas and core samples from Deep Sea Drilling Project/International Phase of Ocean Drilling (DSDP/IPOD) Site 533 on the Blake Outer Ridge in the Northwest Atlantic and Sites 565-570 in the Middle America Trench of the Pacific were obtained for molecular and isotopic analyses. On Leg 76 gas samples were collected from the first successful deployment of a pressure core barrel (PCB) in a hydrate region. The sampling confirmed the presence of gas hydrates. Geochemical evidence for gas hydrates in sediments of the Blake Outer Ridge includes (1) high concentrations of methane, (2) a sediment sample with thin, mat-like layers of white crystals that released a volume of gas twenty times greater than its volume of pore fluid, (3) a molecular distribution of hydrocarbon gases that excluded hydrocarbons larger than isobutane, (4) results from pressure-core barrel experiments, and (5) pore fluid chemistry. The gas was biogenic. In contrast to the finely dispersed hydratesmore » in the Atlantic bottom sediments, gas hydrates were recovered at three sites during Leg 84 in Pacific sediments with massive hydrates being recovered in a 3 meter section at Site 570. Again, hydrate methane appeared to be biogenic.« less
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